On Board Diagnostic (OBD) systems monitor the performance of components of vehicle emissions systems. For example, one OBD system detects leaks in an evaporative emissions system of a vehicle. Typically, an engine malfunction indicator is activated when two consecutive leak tests fail. However, a missing or improperly installed fuel cap will cause the leak test failure to occur. A vehicle owner may have the vehicle serviced when the engine malfunction indicator is activated. Technicians may inefficiently spend time tightening or replacing the fuel cap to solve the problem.
In one conventional method, a controller activates a fuel cap indicator after running a system diagnostic. The fuel cap indicator is tied directly to an engine malfunction indicator. Whenever the engine malfunction indicator is activated due to a leak test failure, the fuel cap indicator is also activated. The diagnostic has no ability to distinguish between a leak that occurs due to a missing or improperly replaced fuel cap and other large leaks that may occur. When the fuel cap is tightened or replaced, the fuel cap indicator could remain activated if the leak test failure occurs for a different reason.
Another method uses a sensor to physically detect when a fuel cap is properly installed. The sensor adds cost to the vehicle. The increased number of parts and wiring also increases warranty claims.